Inner tube coated to prevent buckling



Oct. 19, 1954 c. PETERSON ETAL 2,692,000

INNER TUBE COATED TO PREVENT BUCKLING Filed Sept. 13, 1951 INVENTO LflTf/F 62/ 574 Liv/V HARVA') 5,477!

AGENT Patentecl Oct. 19, 1954 INNER TUBE COATED To PREVENT BUCKLING.

Lester .6. Peterson and Harvey J. Batts, Indianapolis, -'I-nd., assignors to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application September 13, 1951, Serial No.-246,382

2 Claims. 1

This invention relates .to an improved inner tube having a coating .on its .exterior surface to prevent buckling.

At extremely low temperatures, that is, at temperatures of zero or below, inner tubes are subject in use to failure caused by what is known as buckling of the tube. This type of failure is particularly troublesome with synthetic elastomers, especially with butyl rubber, due to the poor low temperature properties of these materials. In particular, elastomers such as butyl exhibit what is known as sluggish retraction at low temperatures, that is, the material after being stretched does not return rapidly to its original state. Because of the failure of the material to recover rapidly, there is developed a sub-permanent set in the inner tube, which is accumulated until an actual fold or buckle is produced in the inner tube within the tire casing. These folds or buckles continually move as the tire rotates, and this movement results in chafing and eventual failure of the tube. The low temperature buckling problem is analyzed in detail in the article Utilization of Butyl Rubber in Automotive Inner Tubes by Buckley et al., Industrial and Engineering Chemistry, vol. 42 No. 12, page 2407 (December 1950), wherein it is pointed out that failures from buckling occur when thetube is operated in subzero service.

In the accompanying drawing, Fig. .1 is a side elevational view of an inner tube showing how the tube is distorted under certain conditions of use, Fig. 2 is a transverse sectional elevational view on a larger scale of a mounted inner tube, showing buckles or folds in the tube, and Fig. 3 is a side elevational view of a tube coated in accordance with the invention.

The manner in which inner tubes develop buckles will be more fully understood from a consideration of Figs. 1 and 2, wherein there is shown an inner tube l having conventional circumferential and transverse venting ridges I I on its outer surface which provide for the escape of air from between the inner tube and a tire casing l2 in which the tube is mounted. At lowtemperatures the material of the tube becomes stiff and fails to retract rapidly as the tube is flexed in use, with the result that the tube slips within the casing. This slippage is both longitudinal and sectional and results in distortion of the tube as indicated by the displacement of the transverse venting ridges 'II in Fig. 1 into a curved path, as distinguished from their normal straight disposition as indicated in Fig. 3. Due to lack of elasticity of the cold stiif tube wall, the shoulder regions of the tube are caused to stretch excessively during the deflection cycle, while the crown area tends to resist (compression stress. Since the recovery strength-:isrlow, an excess of the tube wall material gathers in 2 the crown to form folds :or buckles I3. The folds 13 are free to move within the air cavity M of the tube and rub together as the wheel turns. @Cha-fing .of the folds develops and the result is a 'failure that resembles a pinhole in outside appearance.

It has been discovered that the formation of buckles in inner tubes made from elastomeric materials having poor low temperature properties can 'beeffectively prevented by providing the exterior surface of the tube In with a coating l5 that is moderately adhesive to the interior of the tire casing in which the tube is mounted. The coatings which we have found to be suitable for this purpose are those which are mildly tacky or adhesive under the conditions prevailing at the area of contact between the interior surface of the tire casing and the exterior surface of the inner tube. The ability of such a coating to prevent formation of folds or buckles in the inner tube even at low temperatures apparently arises from the fact that the coating produces increased frictional engagement between the inner tube and the tire casing, and such increased frictional engagement evidently prevents any gathering of the material of the inner tube into folds by maintaining all parts of the surface of the inner tube in firm engagement with the surface of the tire casing.

Compositions which we havefound to .be most effective for thispurpose are those comprised of a major proportion of wax and a minor proportion ofa tacky elastomeric material. Most conveniently, the wax and elastomer are emulsified or dispersed in an aqueous medium for application to the tube surface. A dispersion or emulsion of these materials may be coated on the inner tube by any suitable method, such as by brushing or spraying the composition onto the surface of the tube, or by dipping the tube into a bath of the composition.

A typical exampleof a coating for application .to an inner tube in the manner of the invention is as follows:

Parts by weight The paraiiin wax and the .polyisobutylene are first melted together ,and then added to the remaining ingredients dissolved in water.

tion of the mixture results in a smooth disper- .3 sion which may be applied to the inner tube and dried to form a substantially continuous uniform deposit I5. We have found it preferable to heat the coated surface briefly to a temperature approaching or exceeding the softening point of the deposits, e. g. to a temperature of 220 F. or higher for at least minutes. The deposit is substantially non-tacky, that is, there is insufficient tack at ordinary temperatures to cause the tube to stick to itself when folded, or to stick object'ionably to objects with which it comes in contact. However, under conditions prevailing within the tire assembly the tack or adhesion is effective to create sufiicient frictional resistance between the tube and a casing in which it is mounted to obviate formation of buckles at low temperature.

The composition exemplified above may be modified by use of other tacky elastomers, for example, butyl rubber, in place of or in addition to the polyisobutylene. Also, any suitable conventional emulsifying agent may be substituted for the oleic acid, glyceryl monostearate, and triethanolamine used in the above formulation. In place of emulsifying or dispersing the ingredients to form the coating composition, the ingredients may be dissolved in a suitable solvent.

It is important to note that the coating compositions used in the present invention do not act as strong cements between the tube and the tire casing, that is, there is no difficulty about removing the tube from the tire casing at any time it is desired to do so, since the adhesion of the tube to the casing is only very slight, and when removing the tube it is hardly necessary to use noticeably more than the normal force that would be necessary to remove an uncoated tube.

It has been determined by actual tests that butyl inner tubes, which are normally highly susceptible to failure by low temperature buckling, when coated with the compositions described, are substantially free from any tendency to develop this condition. The invention therefore provides a convenient and economical means for eliminating what has heretofore been a particularly vexing problem to those skilled in the art.

While it is preferred to apply the coating to the inner tube itself, it is also possible to obtain the benefits of the invention in large measure by applying the coating to the interior of the tire casing instead. The resulting film of moderately tacky material interposed between the surface of the inner tube and the surface of the casing provides suflicient frictional engagement between the surfaces to prevent buckling.

The invention is especially applicable to inner tubes made of butyl rubber, in which buckling is ordinarily a particularly troublesome problem.

The mildly adhesive coating is preferably applied to the inner tube or to the interior of the tire casing at the time of completion of the usual steps in manufacture of the inner tube or casing, that is, after the inner tube or casing has been vulcanized and is otherwise ready for shipment from the plant for distribution and sale. Because the coating is only extremely mildly adhesive, the inner tube may be folded and packed in the usual manner Without difliculty from sticking to itself or to its wrapping material. Also, the tack or adhesion of the coating is insufficient to interfere with or cause any difficulty in mounting the tube within the casing. There is substantially no tendency for the adhesive coating to interfere with proper nesting of the tube within the casing.

While the inner tubes or tire casing will generally be coated with a composition according to the invention at the time of manufacture, the invention does not preclude applying and drying the composition just prior to the time the tube or tire is mounted on the wheel for use, and similarly the invention does not preclude applying the composition to tires or tubes which have already been used.

Preferably a formulation having the desired degree of tack for purposes of the invention is obtained by employing as one ingredient an uncured or unvulcanized elastomer, such as polyisobutylene or butyl rubber, which possesses a certain degree of inherent tack when deposited in the form of a coating from a suitable solution or dispersion. When a minor proportion of such an elastomer, for example, about 10 to 40 parts by Weight of elastomer, is admixed with a major proportion of a relatively non-tacky wax, for example, correspondingly about to 60 parts by weight of wax, the coating will have the desired amount of tack without being objectionably sticky or adhesive.

The coating is economical and is easily formulated and applied to the tube in the factory, and the coated tube has a pleasing appearance, usually with a slight gloss, especially when the coating is heated for a short time in accordance with the preferred practice of the invention.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. A butyl rubber elastic inner tube that is ordinarily subject to failure from low temperature buckling by reason of failure of the butyl rubber to recover rapidly when used in a tire casing at subzero temperatures, said tube being coated on its exterior surface with a deposit comprised of from 90 to 60 parts by weight of wax and correspondingly from 10 to 40 parts by weight of an elastomer selected from the group consisting of butyl rubber and polyisobutylene, said deposit being insufficiently tacky at ordinary temperatures to cause the tube to stick to itself when folded or to other objects with which it comes in contact, and said deposit creating frictional resistance between the tube and a tire casing in which it is mounted, whereby failure of the tube from buckling at subzero temperature is prevented.

2. A butyl rubber elastic inner tube as in claim 1, in which the said elastomer of the said coating is polyisobutylene.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Enjay-Vistanex, May 24, 1949, 45 pages, pub. by Enjay Company, Inc., 15 West 51st St., New York 19, N. Y., copyright 1948, pages 41 and 42 cited. 

